Waveguide components are an essential part of modern communication systems. Despite impressive progress in the last few decades in the microwave technology, the important role of waveguide components remains undisputed.
RF (Radio Frequency) filters such as microwave filters are indispensable passive components, in any RF/microwave communication system. Waveguide filters are of particular importance due to their low insertion loss characteristics and high power handling capabilities. However, waveguide filters have the disadvantages of being of large size and having a relatively high weight at lower frequency ranges. Therefore, substantial effort has been made to reduce the size and mass of waveguide filters without degrading their electrical performance; in particular, in terms of insertion loss, out-of-band rejection and/or group delay variation.
To this end, a number of configurations have been developed and reported. These include multimode filters, where at least two modes operating within the same resonant cavity are coupled. This allows one to realize higher order filter without increasing its overall size.
Another class of reduced size waveguide filters utilizes ridge waveguide resonators, where a reduction in size stems from the fact that the cut-off frequency of the dominant mode of the ridge waveguide is lower than that of the rectangular waveguide of the same cross section.
Another class of waveguide filters is the all metal insert partial H-plane waveguide filters. These components offer reduced size and are similar to the all metal insert E-plane filters as they comprise a metal insert running along two halves of a split waveguide enclosure.
Since partial H-plane filter frequency characteristic is determined mainly by a metal insert, only a metal insert needs to be replaced whenever filter requirements are redefined. This means that a set of metal inserts and a common waveguide enclosure is sufficient to cover the frequency plan defined for a system operating in a given frequency band.
Therefore, all metal insert partial H-plane filters can be regarded as an alternative to the standard H-plane waveguide filters when the reduced size is paramount. However, metal insert partial H-plane filters are typically coupled by means of coaxial conductors. As far as system integration is concerned, this can be viewed as a limiting factor of the filter application as many systems require a waveguide connection.
There is thus a need for a reliable low-loss transition component between a single ridge waveguide and a partial H-plane waveguide.